PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

Direct Current and Transient Analysis 147

Example 2.7

Analyze the circuit shown in Figure 2.43 for the case where the applied voltage source

is constant at V 0 = 250 V, but the resistance (R) varies over the range 200 Ω ≤ R ≤ 2 kΩ

in linear increments of 10 Ω. Obtain plots of

1. I versus R


2. PR versus R

MATLAB Solution

>> V = 250;

>> R = 200:10:2000;

>> I = V./R;

>> P = I.*V;

>> plot(R,I*1000,R,P) % current in mA

>> title(‘Current and Power vs Resistance’)

>> xlabel(‘Resistance (Ohms)’), ylabel(‘Current (mA), Power(Watts)’)

>> grid on

>> gtext (‘Current’) % place the text ‘Current’ and ‘Power’

>> gtext (‘Power’) % control text by mouse

>> % plots are shown in Figure 2.45

Note that by increasing R, the current I decreases. Since PR = I^2 R, increasing R dec reases

I, where I is the dominant variable. Then by increasing R, the power PR decreases.

FIGURE 2.44

Plots of Example 2.6.

0 100 200 300 400 500 600 700 800 900 1000

0 100 200 300 400 500 600 700 800 900 1000

Current versus Voltage

Voltage (Volts)

Voltage (Volts)

0

200

400

600

800

1000

0

200

400

600

800

1000

Power versus Voltage

Power (watts)

Current (mA)